(a) Field of the Invention
The present invention relates to a hydraulic control system for a seven-speed automatic transmission for a vehicle.
(b) Description of the Related Art
Typical automatic transmissions include a torque converter and a power train with a multiple speed gear mechanism connected to the torque converter. In addition, a hydraulic control system is provided for the automatic transmission for selectively operating at least one operational element included in the power train according to a running state of the vehicle.
One such automatic transmission includes a power train and a hydraulic control system. The power train includes a compound planetary gear set, formed by combining at least two simple planetary gear sets to achieve the required multiple speeds, and a plurality of friction members. The hydraulic control system selectively operates the friction members of the power train according to driving conditions.
A variety of such power trains and hydraulic control systems have been developed by vehicle manufacturers according to their own schemes. Currently, four-speed automatic transmissions are most often found on the market. However, five-speed and six-speed automatic transmissions have also been realized for enhancement of performance of power transmission and for enhanced fuel mileage of a vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.